GM Corvette 1984-1996 Repair Guide

Alternator

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TESTING



There are many possible ways in which the charging system can malfunction. Often the source of a problem is difficult to diagnose, requiring special equipment and a good deal of experience. However, when the charging system fails completely and causes the dash board warning light to come on or the battery to become dead the following items may be checked:

  1. The battery is known to be good and fully charged.
  2.  
  3. The alternator belt is in good condition and adjusted to the proper tension.
  4.  
  5. All connections in the system are clean and tight.
  6.  

1984 Vehicles
ON-VEHICLE Voltage regulator test

See Figure 1

This test is performed with the alternator installed.

  1. Connect a fast charger and a voltmeter to the battery as shown in the accompanying figure.
  2.  



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Fig. Fig. 1: On vehicle voltage regulator test

  1. Turn the ignition ON , and slowly increase the charge rate. The alternator light in the vehicle will dim at the voltage regulator setting. The voltage regulator setting should be a minimum of 13.5 volts and a maximum of 16.0 volts.
  2.  
  3. This test will work even if the rotor circuit is good, even if the stator rectifier bridge or diode trio is bad.
  4.  

OFF-VEHICLE VOLTAGE REGULATOR TEST

See Figure 2

  1. Connect a voltmeter and a fast charger to a 12-volt battery, as shown in the accompanying figure.
  2.  



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Fig. Fig. 2: Off vehicle voltage regulator test connections

  1. Connect the regulator and test light as shown, observing battery polarity.
  2.  
  3. The test light should be on.
  4.  
  5. Turn the fast charger on, and slowly increase the charge rate. Observe the voltmeter; the light should go out at the voltage regulator setting.
  6.  
  7. The voltage regulator setting should be a minimum of 13.5 volts and a maximum of 16.0 volts.
  8.  

1985-96 Vehicles
Alternator on-vehicle output test

The battery must be fully charged to perform this test.

  1. Connect an ammeter in series at the alternator output "BAT" terminal.
  2.  
  3. Connect the voltmeter and carbon pile across the battery terminals.
  4.  
  5. Operate the engine at a moderate speed. With the carbon pile turned "OFF", check the voltage across the battery terminals:
    1. If the reading is above 16 volts, the alternator must be repaired or replaced.
    2.  
    3. If the reading is below 16 volts, proceed with the test.
    4.  

  6.  
  7. With the engine still operating at moderate speed, turn the accessories ON, and load the battery with the carbon pile to get the maximum alternator output on the ammeter. Maintain the voltage above 13 volts:
    1. If the output is within 15 amperes of the rated output, the alternator is good.
    2.  
    3. If the output is not within 15 amperes of the rated output, repair or replace the alternator.
    4.  

  8.  

alternator bench test

See Figure 3

The alternator must be removed from the vehicle and placed in a suitable test stand to perform this procedure. The battery must be fully charged to perform this test.

  1. Remove the alternator from the vehicle and mount it in a suitable test stand, according to the stands manufacturers instructions. The test stand must be capable of driving the alternator at 6,500 rpm.
  2.  
  3. Make test connections as shown in the accompanying figure, except leave the carbon pile disconnected. The ground polarity of the alternator and battery must be the same. Use a 30-500 ohm resistor between the battery and the "L" terminal of the alternator.
  4.  



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Fig. Fig. 3: Alternator bench check test connections-1985-91 vehicles

  1. Rotate the pulley clockwise, slowly increase the alternator speed to 6500 rpm and observe the voltage.
  2.  
  3. If the voltage is uncontrolled and increases above 16.0 volts, either the rotor field is shorted, the regulator is faulty or both. A shorted rotor field can cause the regulator to malfunction.
  4.  
  5. If the voltage is below 16.0 volts, increase the speed and adjust the carbon pile to obtain maximum amperage output. Maintain the voltage above 13.0 volts.
  6.  
  7. If the output is within 15 amperes of the rated output, the alternator must be repaired or replaced.
  8.  
  9. If the output is not within 15 amperes of the rated output, the alternator must be repaired or replaced.
  10.  

REMOVAL & INSTALLATION




CAUTION
Failure to disconnect the battery cable may result in personal injury. If a tool is shorted at the alternator lead, the tool will heat enough to burn your skin.

5.7L (VIN 8) Engine
1984 vehicles

See Figure 4

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner flex duct.
  4.  
  5. Remove the adjusting brace bolt.
  6.  
  7. Loosen the alternator mounting bolts.
  8.  



Click image to see an enlarged view

Fig. Fig. 4: Exploded view of the alternator mounting-1984 vehicle shown

  1. Position the alternator to ease belt tension, then remove the belt from the alternator pulley.
  2.  
  3. Remove the alternator mounting bracket through bolt, then remove the alternator.
  4.  
  5. Installation is the reverse of the removal procedure.
  6.  

1985-88 vehicles

See Figures 5, 6, 7, 8, 9, 10, 11 and 12

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the 2-terminal plug and battery leads from the back of the alternator.
  4.  



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Fig. Fig. 5: Unfasten the nut securing the battery lead to the rear of the alternator



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Fig. Fig. 6: Unplug the remaining electrical connector from the rear of the alternator

  1. Remove the alterantor bracket bolt.
  2.  
  3. Loosen the alternator-to-air pump bracket bolt, then swing the bracket aside.
  4.  



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Fig. Fig. 7: Loosen the bolt securing the bracket to the air pump ...



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Fig. Fig. 8: ... then swing the bracket up and away from the alternator

  1. Unfasten the bolt securing the alternator brace to the rear of the alternator.
  2.  



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Fig. Fig. 9: Remove the alternator-to-brace bolt

  1. Loosen the bolts, then remove the alternator drive belt.
  2.  



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Fig. Fig. 10: Loosen the bolts and unroute the drive belt from the alternator pulley

  1. Unfasten the alternator mounting through bolts, then remove the alternator from the vehicle.
  2.  



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Fig. Fig. 11: Remove the alternator through bolt ...



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Fig. Fig. 12: ... then remove the alternator from the vehicle

  1. Installation is the reverse of the removal procedure.
  2.  

1989-91 Vehicles

See Figure 13

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the regulator connector and battery lead from the back of the alternator.
  4.  
  5. Remove the serpentine drive belt, using a 1 / 2 in. breaker bar to rotate the tensioner.
  6.  
  7. Remove the alternator mounting bolts, then remove the alternator from the vehicle. If installing a new alternator, transfer the brackets to the new alternator.
  8.  



Click image to see an enlarged view

Fig. Fig. 13: Exploded view of the alternator and related components-1989-91 5.7L (VIN G) engines

To install:
  1. Position the alternator in the vehicle. Install the lower mounting bolt finger-tight.
  2.  
  3. Install the upper alternator mounting bolt and tighten finger-tight.
  4.  
  5. Position the alternator brace onto the rear of the alternator, then install the brace bolt finger-tight.
  6.  
  7. Tighten the alternator bolts as follows:
    1. Lower mounting bolt: 37 ft. lbs. (50 Nm).
    2.  
    3. Upper mounting bolt: 37 ft. lbs. (50 Nm).
    4.  
    5. Brace bolt: 17 ft. lbs. (23 Nm).
    6.  

  8.  
  9. Install the serpentine drive belt.
  10.  
  11. Attach the regulator connector and battery lead to the back of the alternator.
  12.  
  13. Connect the negative battery cable.
  14.  

5.7L (VIN J) Engine

See Figure 14

1990 vehicles
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air intake duct and the throttle body extension.
  4.  
  5. Remove the accelerator and cruise control cable clamps from the plenum.
  6.  
  7. Remove the throttle body, gasket and electrical connectors.
  8.  
  9. Position the throttle body aside with the cables attached.
  10.  
  11. Unfasten the water pump pulley bolts.
  12.  
  13. Remove the water pump pulley and serpentine belt by releasing the belt tension.
  14.  
  15. Remove the alternator support bracket.
  16.  
  17. Remove the alternator lower mounting bolt.
  18.  
  19. Remove the engine oil temperature sensor.
  20.  
  21. Detach the alternator electrical connectors, then remove the alternator from the vehicle.
  22.  

To install:
  1. Attach the electrical connectors to the alternator, then position the alternator into the vehicle.
  2.  
  3. Apply Loctite® 565 to the threads of the lower mounting bolts, then install the bolts and tighten to 16 ft. lbs. (26 Nm).
  4.  
  5. Apply Loctite® 565 to the threads of the alternator support bracket, then install then bolts and tighten to 19 ft. lbs. (26 Nm).
  6.  
  7. Install the engine oil temperature sensor, making sure to use the proper sealer when installing the sensor.
  8.  
  9. Install the water pump pulley by releasing the belt tension and positioning the pulley onto the water pump flange. Install the pulley bolts and tighten to 89 inch lbs. (10 Nm).
  10.  
  11. Position the throttle body gasket, then install the throttle body. Tighten the throttle body-to-plenum bolts to 11 ft. lbs. (15 Nm).
  12.  
  13. Secure the accelerator and cruise control cable clamps onto the plenum.
  14.  
  15. Install the throttle body extension and tighten the bolts to 53 inch lbs. (6 Nm).
  16.  
  17. Check the serpentine belt tension, as outlined in General Information & Maintenance of this repair guide.
  18.  
  19. Install the air intake duct, then connect the negative battery cable.
  20.  



Click image to see an enlarged view

Fig. Fig. 14: Exploded view of the alternator and bracket mounting-5.7L (VIN J) engine

1991-95 vehicles
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air intake duct and the throttle body extension.
  4.  
  5. Remove the serpentine drive belt.
  6.  
  7. Remove the alternator lower mounting bolt and note the length.
  8.  
  9. Remove the alternator lower support bracket bolts and note the bolt lengths.
  10.  
  11. Remove the upper support bolts, noting the length, and remove the shield.
  12.  
  13. Remove the rear support brace.
  14.  
  15. Detach the oil sender electrical connector, then remove the sender.
  16.  
  17. Unplug the regulator connector and unscrew battery-to-alternator terminal, then remove the alternator from the vehicle.
  18.  

To install:
  1. Attach the regulator connector and the battery-to-alternator terminal ("BAT" terminal), then position the alternator in the vehicle. Tighten the "BAT" terminal nut to 71 inch lbs. (8 Nm). Do NOT overtighten.
  2.  
  3. Install the oil sender and attach the electrical connector.
  4.  
  5. Apply Loctite® 565, or equivalent sealant, to all of the mounting bolt threads.
  6.  
  7. Install the rear support brace and bolt. Tighten the bolt to 17 ft. lbs. (23 Nm).
  8.  
  9. Instlal the upper support bracket and bolts.
  10.  
  11. Install the lower support bracket, spacer, support bolts and mounting bolt.
  12.  
  13. Tighten the upper support and lower mounting bolts to 38 ft. lbs. (52 Nm).
  14.  
  15. Tighten the lower support bracket bolts to 19 ft. lbs. (26 Nm).
  16.  
  17. Install the serpentine drive belt.
  18.  
  19. Install the throttle body extension and tighten the bolts to 53 inch lbs. (6 Nm).
  20.  
  21. Install the air intake duct and connect the negative battery cable.
  22.  

5.7L (VIN P and 5) Engines

See Figures 15 and 16

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air intake duct.
  4.  
  5. Unplug the regulator connector, and remove the battery-to-alternator terminal from the back of the alternator.
  6.  



Click image to see an enlarged view

Fig. Fig. 15: Detach the regulator connector, and disconnect the "BAT" cable from the terminal

  1. Remove the serpentine drive belt by releasing the belt tension.
  2.  
  3. Remove the alternator rear mounting bolt, nut and alternator rear mounting bracket.
  4.  
  5. Unfasten the 2 alternator upper mounting bolts, and remove the alternator upper mounting bracket.
  6.  
  7. Remove the two lower alternator mounting bracket bolts, then remove the lower bracket.
  8.  
  9. Remove the alternator from the vehicle.
  10.  



Click image to see an enlarged view

Fig. Fig. 16: Exploded view of the alternator and related components-5.7L (VIN P & 5) engines

To install:
  1. Position the alternator in the vehicle.
  2.  
  3. Instlal the lower mounting bracket and the two lower mounting bolts. Do NOT tighten the bolts at this time.
  4.  
  5. Install the upper mounting bracket and two retaining bolts. Do NOT tighten the bolts at this time.
  6.  
  7. Install the rear mounting bracket and mounting bolt.
  8.  
  9. Tighten the bolts, as follows:
    1. Alternator lower and upper mounting bolts: 37 ft. lbs. (50 Nm).
    2.  
    3. Alternator rear mounting bolt: 17 ft. lbs. (23 Nm).
    4.  
    5. Alternator rear mounting nut: 24 ft. lbs. (33 Nm).
    6.  

  10.  
  11. Install the serpentine drive belt.
  12.  
  13. Attach the electrical connector to the alternator.
  14.  
  15. Connect the battery-to-alternator terminal to the back of the alternator. Tighten the "BAT" terminal nut to 71 inch lbs. (8 Nm). Do NOT overtighten.
  16.  
  17. Install the air intake duct.
  18.  
  19. Connect the negative battery cable. Tighten the cable bolt/screw to 11 ft. lbs. (15 Nm).
  20.  

 
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